The terminal latency of the phrenic nerve correlates with respiratory symptoms in amyotrophic lateral sclerosis

- The prolonged terminal latency of the phrenic nerve may reflect a distal axonopathy.
- The optimal cutoff value for the terminal latency of the phrenic nerve was 7.65 ms.
- Recognizing the usefulness of the terminal latency of the phrenic nerve in ALS is important.

ObjectiveThe aim of the study was to investigate the electrophysiological parameters in phrenic nerve conduction studies (NCS) that sensitively reflect latent respiratory insufficiency present in amyotrophic lateral sclerosis (ALS).MethodForty-nine patients with ALS were examined, and after exclusion, 21 patients with ALS and their phrenic NCS results were reviewed. The patients were divided into two groups according to their respiratory sub-score in the ALS functional rating scale - revised (Group A, sub-score 12 vs. Group B, sub-score 11). We compared the parameters of phrenic NCS between the two groups.ResultsThere were no significant differences in the clinical characteristics between the two groups. Using a multivariate model, we found that the terminal latency of the phrenic nerve was the only parameter that was associated with early symptoms of respiratory insufficiency (p < 0.05). The optimal cutoff value for the terminal latency of the phrenic nerve was 7.65 ms (sensitivity 80%, specificity 68.2%).ConclusionThe significantly prolonged terminal latency of the phrenic nerve in our study may reflect a profound distal motor axonal dysfunction of the phrenic nerve in patients with ALS in the early stage of respiratory insufficiency that can be used as a sensitive electrophysiological marker reflecting respiratory symptoms in ALS.SignificanceThe terminal latency of the phrenic nerve is useful for early detection of respiratory insufficiency in patients with ALS.